Using bacteria to detect toxins in water

translation of synthetic biology research into technology for improving human health.”

The release notes that the development of the techniques to make the sensor and the flashing display built on the work of scientists in the Division of Biological Sciences and School of Engineering, which they published in two previous Nature papers over the past four years. In the first paper, the scientists demonstrated how they had developed a way to construct a robust and tunable biological clock to produce flashing, glowing bacteria. In the second paper, published in 2010, the researchers showed how they designed and constructed a network, based on a communication mechanism employed by bacteria, that enabled them to synchronize all of the biological clocks within a bacterial colony so that thousands of bacteria would blink on and off in unison.

“Many bacteria species are known to communicate by a mechanism known as quorum sensing, that is, relaying between them small molecules to trigger and coordinate various behaviors,” said Hasty, explaining how the synchronization works within a bacterial colony. “Other bacteria are known to disrupt this communication mechanism by degrading these relay molecules.”

The researchers, however, found the same method could not be used to instantaneously synchronize millions of bacteria from thousands of colonies.

“If you have a bunch of cells oscillating, the signal propagation time is too long to instantaneously synchronize 60 million other cells via quorum sensing,” said Hasty. But the scientists discovered that each of the colonies emit gases that, when shared among the thousands of other colonies within a specially designed microfluidic chip, can synchronize all of the millions of bacteria in the chip. “The colonies are synchronized via the gas signal, but the cells are synchronized via quorum sensing. The coupling is synergistic in the sense that the large, yet local, quorum communication is necessary to generate a large enough signal to drive the coupling via gas exchange,” added Hasty.

Graduate students Arthur Prindle, Phillip Samayoa and Ivan Razinkov designed the microfluidic chips, which for the largest ones, contain 50 to 60 million bacterial cells and are about the size of a paper clip or a microscope cover slip. The smaller microfluidic chips, which contain approximately 2.5 million cells, are about a tenth of the size of the larger chips.

Each of the blinking bacterial colonies comprise what the researchers call a “biopixel,” an individual point of light much like the pixels on a computer monitor or television screen. The larger microfluidic chips contain about 13,000 biopixels, while the smaller chips contain about 500 pixels.

Hasty said he believes that within five years, a small hand-held sensor could be developed that would take readings of the oscillations from the bacteria on disposable microfluidic chips to determine the presence and concentrations of various toxic substances and disease-causing organisms in the field.

Other UC San Diego scientists involved in the discovery were Tal Danino and Lev Tsimring.

The release also notes that the UC San Diego Technology Transfer Office has filed a patent application on the Hasty group’s invention. The University says that companies that have a commercial interest in the research or application should contact the office.

— Read more in Arthur Prindle, “A sensing array of radically coupled genetic ‘biopixels’,” Nature (18 December 2011) (doi:10.1038/nature10722)